Revert "remove false BUG_ON() from run_posix_cpu_timers()"

This reverts commit 3de463c7.

Roland has another patch that allows us to leave the BUG_ON() in place
by just making sure that the condition it tests for really is always
true.

That goes in next.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/exit.c

@@ -825,6 +825,14 @@ fastcall NORET_TYPE void do_exit(long code)
 
 	tsk->flags |= PF_EXITING;
 
+	/*
+	 * Make sure we don't try to process any timer firings
+	 * while we are already exiting.
+	 */
+ 	tsk->it_virt_expires = cputime_zero;
+ 	tsk->it_prof_expires = cputime_zero;
+	tsk->it_sched_expires = 0;
+
 	if (unlikely(in_atomic()))
 		printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",
 				current->comm, current->pid,

kernel/posix-cpu-timers.c

@@ -1293,11 +1293,12 @@ void run_posix_cpu_timers(struct task_struct *tsk)
 
 #undef	UNEXPIRED
 
+	BUG_ON(tsk->exit_state);
+
 	/*
 	 * Double-check with locks held.
 	 */
 	read_lock(&tasklist_lock);
-	if (likely(tsk->signal != NULL)) {
 	spin_lock(&tsk->sighand->siglock);
 
 	/*
@@ -1316,7 +1317,6 @@ void run_posix_cpu_timers(struct task_struct *tsk)
 	 * spin until we've taken care of that timer below.
 	 */
 	spin_unlock(&tsk->sighand->siglock);
-	}
 	read_unlock(&tasklist_lock);
 
 	/*